Description Expecto Patronum
The incantation "Expecto Patronum" uses the power of the wizard's strong positive memories and feelings to summon a protective spirit that shields against threatening beings and creatures. Thus, the summoning of the Patronus is one of the most powerful, yet also one of the most difficult spells to perform. According to Remus Lupin, it even far exceeds the level of the OWL (Outstanding Wizard Level) exams. Nonetheless, Harry Potter, as the youngest wizard to date, managed to summon such a Patronus in 1994, during his third year at school.
On this shirt, you can see Harry's personal Patronus, which, like those of his parents, takes the form of a stag and thus is a symbol for the Potter family.